U.S. patent application number 13/010831 was filed with the patent office on 2012-01-12 for induction heating-assisted vibration welding method and apparatus.
This patent application is currently assigned to GM GLOBAL TECHNOLOGY OPERATIONS LLC. Invention is credited to Wayne W. Cai, Hua-Tzu Fan, Paul F. Spacher.
Application Number | 20120006810 13/010831 |
Document ID | / |
Family ID | 45403142 |
Filed Date | 2012-01-12 |
United States Patent
Application |
20120006810 |
Kind Code |
A1 |
Fan; Hua-Tzu ; et
al. |
January 12, 2012 |
INDUCTION HEATING-ASSISTED VIBRATION WELDING METHOD AND
APPARATUS
Abstract
A method for heating a work piece or a welding interface using a
vibration welding system includes positioning the work piece
adjacent to a welding tool such that the welding interface is also
adjacent to the welding tool, and then using an induction heating
device to generate an eddy current in one of the welding tool and
the work piece to thereby heat the welding interface to a
calibrated threshold temperature or temperature range. A
high-frequency vibration thereafter may be applied using a
sonotrode of the vibration welding system to form a weld. The
method may include adjusting the position and orientation of the
induction heating device relative to the work piece to change the
location of the eddy current. A vibration welding system includes a
welding tool, the induction heating device, and a control module
which controls the induction heating device to thereby control the
welding temperature.
Inventors: |
Fan; Hua-Tzu; (Troy, MI)
; Cai; Wayne W.; (Troy, MI) ; Spacher; Paul
F.; (Rochester, NY) |
Assignee: |
GM GLOBAL TECHNOLOGY OPERATIONS
LLC
Detroit
MI
|
Family ID: |
45403142 |
Appl. No.: |
13/010831 |
Filed: |
January 21, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61363022 |
Jul 9, 2010 |
|
|
|
Current U.S.
Class: |
219/617 |
Current CPC
Class: |
B29C 66/81433 20130101;
B23K 13/01 20130101; B29C 65/08 20130101; B29C 66/91221 20130101;
B29C 66/91651 20130101; B23K 2103/10 20180801; B29C 66/73921
20130101; B29C 65/06 20130101; B23K 2103/12 20180801; B29C 66/9517
20130101; B23K 20/106 20130101; B29C 66/43 20130101; B29C 65/18
20130101; B29C 66/91231 20130101; B29C 66/1122 20130101; B29C
66/9512 20130101; B29C 65/32 20130101; B29C 66/9516 20130101; B29C
66/0242 20130101; B29C 66/81871 20130101; B29C 65/72 20130101; B23K
2101/38 20180801; B29C 66/91212 20130101; B29C 65/36 20130101; B29C
66/9513 20130101; B29C 66/8167 20130101; B29C 66/81811
20130101 |
Class at
Publication: |
219/617 |
International
Class: |
B23K 13/01 20060101
B23K013/01 |
Claims
1. A vibration welding method comprising: positioning a work piece
adjacent to a welding tool, such that the work piece defines a
welding interface adjacent to the welding tool; using an induction
heating device to generate an eddy current in one of the welding
tool and the work piece to thereby heat the work piece or the
welding interface, via conduction, to a calibrated threshold
temperature; and forming a weld using vibrations from a sonotrode
after the work piece or welding interface reaches the calibrated
threshold temperature.
2. The method of claim 1, further comprising: embedding the
induction heating device within the welding tool.
3. The method of claim 2, wherein embedding the induction heating
device within the welding tool includes embedding the induction
heating device in an anvil head.
4. The method of claim 1, wherein using an induction heating device
to generate an eddy current includes: automatically modulating an
alternating current (AC) electrical signal to generate a modulated
AC electrical signal; and transmitting the modulated AC electrical
signal to the induction heating device via a control module.
5. The method of claim 1, wherein positioning the work piece
includes positioning a conductive interconnect member and a
conductive tab of a battery adjacent to a stationary welding
anvil.
6. The method of claim 1, further comprising: adjusting the
position of the induction heating device relative to the work piece
to thereby change the location of the eddy current with respect to
the work piece.
7. A vibration welding system for welding adjacent surfaces of a
work piece using vibration energy, the welding system comprising: a
welding tool; an induction heating device configured for heating
the work piece or a welding interface defined by the adjacent
surfaces of the work piece; and a control module configured to
control an operation of the induction heating device to thereby
control the welding temperature at or along the welding interface
to a calibrated threshold temperature.
8. The welding system of claim 7, wherein the induction heating
device includes at least one induction coil positioned within a
channel defined by the welding tool.
9. The welding system of claim 7, wherein the induction heating
device includes an insulating layer positioned between the at least
one induction coil and the work piece.
10. The welding system of claim 7, wherein the induction heating
device is connected to a welding power supply via one of an
insulated silver wire and an insulated copper wire, and the work
piece is one of a copper and an aluminum conductive tab of a
battery.
11. The welding system of claim 7, wherein the control module is
configured to automatically modulate an alternating current (AC)
electrical signal to generate a modulated AC electrical signal
having a frequency of at least approximately 25 KHz, and to
transmit the modulated AC electrical signal to the induction
heating device.
12. An anvil assembly for use as a welding tool in a vibration
welding system, wherein the vibration welding system is configured
for welding adjacent surfaces of a work piece using vibration
energy, the anvil assembly comprising: an anvil body; an anvil head
operatively connected to the anvil body; and an induction heating
device configured for heating the work piece or a welding interface
defined by the adjacent surfaces of the work piece; wherein the
induction heating device is configured to increase a welding
temperature at or along the welding interface to a calibrated
threshold temperature.
13. The anvil assembly of claim 12, wherein the induction heating
device includes an induction coil positioned within a channel
defined by the anvil head.
14. The anvil assembly of claim 12, wherein the induction heating
device further includes an insulating layer positioned between the
at least one induction coil and the work piece.
15. The anvil assembly of claim 12, wherein the induction heating
device receives a modulated AC electrical signal having a frequency
of at least approximately 25 KHz from a control module of the
welding system, and increases the welding temperature in response
to the modulated AC electrical signal.
16. The anvil assembly of claim 12, wherein the vibration welding
system is configured for simultaneously forming a plurality of weld
spots when welding the adjacent surfaces of the work piece, further
comprising: a plurality of the induction heating devices that is
equal to the number of the plurality of weld spots.
17. The anvil assembly of claim 12, wherein the work piece is
copper conductive battery tab that is approximately 0.2 centimeters
thick.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. Provisional
Patent Application No. 61/363,022, filed Jul. 9, 2010, which is
hereby incorporated by reference in its entirety.
TECHNICAL FIELD
[0002] The present invention relates to an induction
heating-assisted vibration welding method and apparatus.
BACKGROUND
[0003] The process of vibration welding can be used to securely
join adjacent surfaces of one or more work pieces. A weld is formed
by applying vibrations to the work piece in a calibrated range of
frequencies and directions. The work piece is first positioned and
clamped between a stationary anvil and a welding horn or sonotrode.
When energized, the sonotrode transmits vibration energy through
the work piece. Heat generated by the friction softens the material
of the work piece along the interfacing surfaces, which ultimately
forms a solid weld. The efficiency, consistency, and
reliability/durability of a vibration-welded part depend largely on
the design of the sonotrode, the anvil, and various other welding
tools and control equipment used to form the welds.
SUMMARY
[0004] A vibration welding method and system are provided for
increasing a temperature of a selected portion of a work piece or
multiple work pieces, and/or a selected welding interface defined
by the work piece(s), during a vibration welding process. The
method includes heating the selected portion or welding interface
using an induction heating device, which may be embedded within a
welding anvil or another designated welding tool in one possible
embodiment. The position and/or orientation of the induction
heating device relative to the work piece determines the position
of a generated eddy current with respect to the same work piece,
and thus determines the particular welding interface to be
heated.
[0005] In a vibration welding process, the temperature in a weld
zone drops as heat energy from the vibrations of the sonotrode
dissipates. Even if equal amounts of heat can be generated at each
of the different possible welding interfaces for a given
multiple-sheet welding configuration, the welding temperature at a
given welding interface may differ drastically from that of other
interfaces. This is largely due to different friction conditions,
different relative motion between the surfaces of the work piece,
and heat sink effects. Therefore, a designated portion of the work
piece, such as the thickest portion of the work piece or the
surface or component of the work piece having the highest thermal
conductivity, can be selectively heated via induction as set forth
herein using the induction heating device.
[0006] In particular, a method is disclosed herein for heating of a
work piece and/or a welding interface formed using a vibration
welding system, wherein the welding interface is defined by
adjacent surfaces of a work piece being welded. The method includes
positioning the work piece adjacent to a welding tool such that the
welding interface is also adjacent to the welding tool, and then
using an induction heating device to generate an eddy current in
one of the welding tool and the work piece. Once the eddy current
is generated within all conductors in an electromagnetic field
surrounding the energized induction heating device, the welding
interface is heated to a calibrated threshold temperature via
conduction, or to within a calibrated temperature range. The work
piece may thereafter be vibration welded using a sonotrode of the
vibration welding system, either concurrently or after the
aforementioned heating step.
[0007] Additionally, a vibration welding system for welding
adjacent surfaces of a work piece using vibration energy includes a
welding tool, an induction heating device embedded within the
welding tool, and a controller. The induction heating device, once
energized, generates eddy current(s) sufficient for heating a
welding interface defined by adjacent surfaces of the work piece.
The controller modulates the current and the frequency transmitted
to the induction heating device to maintain the welding temperature
above a calibrated threshold. The design, position, and orientation
of the induction heating device ultimately determine whether the
welding tool or the work piece is most thoroughly heated.
[0008] The above features and advantages and other features and
advantages of the present invention are readily apparent from the
following detailed description of the best modes for carrying out
the invention when taken in connection with the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1 is a schematic side view illustration of a vibration
welding system having an induction heating device as disclosed
herein;
[0010] FIG. 2 is a perspective side view illustration of a welding
tool having an embedded induction heating device according to one
possible embodiment;
[0011] FIG. 3 is schematic side view illustration of the welding
tool of FIG. 2 being used to form a weld in a work piece;
[0012] FIG. 4 is a perspective side view illustration of a welding
tool having an embedded induction heating device according to
another possible embodiment; and
[0013] FIG. 5 is a flow chart describing a method for heating a
welding interface during a vibration welding process using the
system shown in FIG. 1.
DESCRIPTION
[0014] Referring to the drawings, wherein like reference numbers
refer to like components, and beginning with FIG. 1, a vibration
welding system 10 is configured for forming a weld using ultrasonic
vibrations, or using vibrations of other suitable frequencies.
Localized heating is provided via one or more induction heating
devices 40. Each induction heating device 40 is used to heat a work
piece 28, which while used in the singular herein may include
multiple pieces. The induction heating device 40 raises a welding
temperature via conduction at or along one or more welding
interfaces 26, i.e., the interfacing adjacent surfaces of the work
piece(s) 28 which are to be welded together. Heating of a welding
tool such as an anvil assembly 30 is one possible way of heating
the welding interface(s) 26, as noted below with reference to FIGS.
2 and 3, with the ultimate goal of heating the work piece 28 and a
particular welding interface.
[0015] The welding system 10 may include welding control equipment
12. The welding control equipment 12 includes a welding power
supply 14 operable for transforming an available source power into
a form readily usable in vibration welding. As understood by those
of ordinary skill in the art, a welding power supply used in a
vibration welding process, such as the welding power supply 14
shown in FIG. 1, can be electrically-connected to any suitable
energy source, e.g., a 50-60 Hz wall socket. The welding power
supply 14 may include a welding controller 16, which is usually but
not necessarily integrally included within the welding power
supply.
[0016] The welding power supply 14 and the welding controller 16
ultimately transform source power into a suitable power control
signal having a predetermined waveform characteristic(s) suited for
use in the vibration welding process, for example a frequency of
several hertz (Hz) to approximately 40 KHz, or much higher
frequencies depending on the particular application. The power
control signal is transmitted from the welding power supply 14 or
the welding controller 16 to a converter 18 having the required
mechanical structure for producing a mechanical vibration in one or
more welding pads 22. The welding pads 22 may be integrally-formed
with or connected to a vibrating welding horn or sonotrode 24.
[0017] The vibration welding system 10 may also include a booster
20. The booster 20 may be any device configured for amplifying the
amplitude of vibration, and/or for changing the direction of an
applied clamping force. That is, a vibration signal from the
welding controller 16 may have a relatively low amplitude
initially, e.g., a fraction of a micron up to a few millimeters,
which can then be amplified via the booster 20 to produce the
required mechanical oscillation. The vibration signal is in turn
transmitted to the one or more welding pads 22 of the sonotrode
24.
[0018] A weld is ultimately formed at or along welding interfaces
26 between adjacent surfaces of the work piece 28. The welding
system 10 may be used to weld or join metals or thermoplastics by
varying the orientation of the vibrations emitted by the sonotrode
24. That is, for thermoplastics the vibrations emitted by the
sonotrode 24 tend to be perpendicular to the surface being welded,
while for metals the direction may be generally tangential
thereto.
[0019] Still referring to FIG. 1, each welding pad 22 may have
knurls 27, i.e., textured surfaces contacting the work piece 28
during formation of a weld at or along the welding interface 26.
The knurls 27 may be textured or configured as raised teeth and/or
other frictional patterns providing a sufficient grip on the work
piece 28 when the work piece is clamped. To further facilitate the
welding process, the work piece 28 is positioned adjacent to the
anvil assembly 30. The anvil assembly 30 may include a welder body
32, an anvil body 34, and an anvil head 36. The anvil head 36 may
have knurls 38 that are similar in construction to the knurls 27 of
the welding pad 22 as described above.
[0020] The induction heating device 40 is used to heat the work
piece 28 and/or the welding interface 26, i.e., a designated
interfacing surface of the work piece to be welded. That is, the
work piece 28 may define multiple welding interfaces 26 as shown in
FIG. 1, with the innermost weld location indicated in FIG. 1 by
arrow 33. The induction heating device 40 may be positioned with
respect to the work piece 28, e.g., surrounding the work piece. The
induction heating device 40 may be alternately embedded as shown at
various positions and/or orientations within a designated welding
tool, e.g., a portion of the sonotrode 24 and/or portions of the
anvil assembly 30.
[0021] Additionally, the position and/or orientation of the
induction heating device 40 relative to the work piece 28 defining
the welding interface 26 may be selected to thereby determine the
position and orientation of an eddy current (arrow 41) generated by
the induction heating device when the device is energized. The eddy
current (arrow 41) ultimately heats the conductive metal materials
within which the eddy current is generated, e.g., the anvil head 36
or the work piece 28.
[0022] The work piece 28 shown in the particular embodiment shown
in FIG. 1 may include conductive tabs 42 of a multi-cell battery
44, only the top or interconnect board of which is shown in FIG. 1
for simplicity. The battery 44 may be used for electric propulsion
of a vehicle (not shown), and may include a conductive bus bar or
interconnect member 46. The interconnect member 46 may have side
rails 48 that are connected to each other by a cross member 49. In
this embodiment, the conductive tabs 42 form electrode extensions
of respective battery cells, and are each internally-welded to the
various anodes and cathodes comprising that particular cell as will
be well understood by those of ordinary skill in the art. The
interconnect member 46 may be constructed of a suitable conductive
material, e.g., copper, and may be shaped, sized, and/or otherwise
configured to form a rail or bus bar, and mounted to the battery
44.
[0023] Potential uses for the battery 44 include the powering of
various onboard electronic devices and propulsion in a hybrid
electric vehicle (HEV), an electric vehicle (EV), a plug-in hybrid
electric vehicle (PHEV), and the like. By way of example, the
battery 44 could be sufficiently sized to provide the necessary
voltage for powering an electric vehicle or a hybrid
gasoline/electric vehicle, e.g., approximately 300 to 400 volts or
another voltage range, depending on the required application.
[0024] As the sonotrode 24 of FIG. 1 clamps against the anvil
assembly 30 and traps the work piece 28, the sonotrode vibrates at
a calibrated frequency and amplitude to generate friction and heat
along the welding interfaces 26. However, the anvil assembly 30 can
act as a substantial heat sink, and therefore heat is lost as
energy is transmitted from the sonotrode 24 toward the anvil
assembly. Potentially, the innermost weld, indicated by arrow 33 in
FIG. 1, i.e., the farthest weld spot away from the sonotrode 24,
has the lowest relative temperature, and hence potentially forms
the weakest bond. This effect can be counteracted by heating the
welding interface(s) 26 as disclosed below.
[0025] Referring to FIG. 2, the induction heating device(s) 40 may
be embedded within one or more welding tools of the welding system
10 shown in FIG. 2 in one embodiment. Three induction heating
devices 40 are shown in FIG. 2 to correspond to three different
weld spots in one possible embodiment. The number of induction
heating devices 40 used in a particular embodiment may vary. For
example, the anvil body 34 may define a channel 51 (see FIG. 3) in
which a corresponding one of the induction heating device 40 are
positioned. Since the anvil head 36 is relatively small, the
induction heating devices 40 may be sized accordingly, e.g., the
channel 51 of FIG. 3 may be approximately 8 mm in diameter in one
embodiment, with the induction heating device sized to fit within
this diameter.
[0026] The induction heating device 40 is electrically connected to
the welding power supply 14 or to another 110V or 220V power supply
via a control module 50 and wires 52. The wires 52 may be
constructed of insulated silver (Ag) or insulated copper (Cu)
according to one possible embodiment, thereby optimizing energy
transfer to the induction heating device 40. Such an embodiment may
be of particular benefit when welding copper or aluminum, e.g., the
conductive tabs 42 of the battery 44 shown in FIG. 1. The welding
interface 26 at the innermost weld, as indicated by arrow 33 in
FIG. 1, tends to have the weakest bonding strength. An eddy current
(arrow 41) is therefore centered on that particular location in
order to produce a better bond between welded surfaces of the work
piece 28.
[0027] Also, the control module 50 may be used to modulate the
electrical current and frequency of an alternating current (AC)
signal (arrow 53) transmitted to the induction heating device 40.
Use of a high frequency AC current, e.g., approximately 25 kHz or
higher, may facilitate generation of the eddy current (arrow 41) in
the work piece 28 of FIG. 1, and/or the anvil head 36, or in
another welding tool containing the induction heating device 40.
The control module 50 may be part of the welding controller 16
shown in FIG. 1, or it may be a separate control device. The
control module 50 regulates the welding temperature by controlling
the properties of the AC power signal 53 delivered to the induction
heating device 40. The anvil body 34 is also shown with the anvil
head 36 and knurls 38, as well as with a plurality of mounting
holes 56 which receive fasteners (not shown). In this manner, the
anvil body 34 may be mounted to the welder body 32 shown in FIG.
1.
[0028] Sizing of the induction heating device 40 may be determined
by the nature of the immediate welding task. For example, heating
up a copper work piece having an area of 1 cm.times.1 cm.times.0.20
cm, which is approximately four times the area of a typical weld
spot, within 1 second (s) requires, according to one possible
formula, power (P) of Vc.sub.v.DELTA.T/t, where V is the volume of
the work piece (in m.sup.3), c.sub.v is the volumetric specific
heat capacity in Joules (J)/centimeter (cm).sup.3 Kelvin (K), t=1
s, and .DELTA.T=130.degree. K, i.e., the desired increase in
welding temperature.
[0029] The magnetic flux density (B) required to deliver the
required power (P) via the eddy current (arrow 41) may be
calculated as: B= {square root over (6.rho.D)}/(.pi.df), where
.rho. is the static resistivity of the material being welded, in
this example copper, D is the penetration depth of the weld, d is
the sheet thickness, and f is the frequency in Hz. The electrical
current (I) required to generate the flux density (B) can be
determined using the equation: I=FBh/.mu.N, where F is a calibrated
safety factor, h is the magnetic flux loop height at the
penetration depth (D), .mu. is the permeability of air, and N is
the number of loops in the induction heating device 40 at the
stated safety factor (F).
[0030] From the stated formulas, which are indeed to be exemplary
and not necessarily applicable to all possible applications, even
given a conservative safety factor (F) of 10 when welding a
relatively thin copper sheet (d=0.001 m) with a weld penetration
depth (D) of 0.0005 m, at a frequency (f) of 25 kHz, the electrical
current (I) required for generating eddy currents (arrow 41)
collectively providing sufficient heating is less than
approximately 5 mA. This low level of electrical current can
provide cost advantageous improvement in the resultant weld quality
of certain welding applications.
[0031] Referring to FIG. 3, the induction heating device 40 may
include induction coils 59, which are insulated from each other,
and a suitable insulator end 58 such as a glass or ceramic layer,
disc, or cylinder. The location of the eddy current (arrow 41)
generated by the induction coils 59 is shown in FIG. 3 within the
anvil head 36, which is just one possible embodiment. Such an
embodiment would tend to heat the anvil head 36, with this heat
being transferred via conduction to the work piece 28 when the
anvil head 36 contacts the work piece. The work piece 28 of FIG. 3
is shown as a three-piece stack up, which depending on the
embodiment may or may not include the tabs 42 of FIG. 2 and the
side rail 48 shown in that Figure.
[0032] The location of the eddy current (arrow 41) may be varied
toward and, if desired, into the work piece 28 simply by
positioning the induction coils 59 closer to the work piece, i.e.,
by moving the coils in the direction of arrow 60. The induction
coils 59 may be hollow tubes to allow for fluid cooling or may be
cooled by other means to prevent overheating. One embodiment
extends the channel 51 deeper into the anvil head 36 to allow
closer fixed positioning of the induction coils 59 with respect to
the work piece 28. Positioning of the induction coils 59 is
variable within the extended channel 51 in another embodiment. For
example, the insulator ends 58 of different thicknesses could be
inserted into the channel 51 to vary the distance between the
induction coils 59 and the welding interface 26 being welded to
form a given weld 54.
[0033] Referring to FIG. 4, in an alternate embodiment an induction
heating device 140 may include partial or full loops 159 arranged
in electrical series from a single length of wire. Each of the
loops 159 may be positioned and oriented to at least partially
circumscribe a center point 70 of a weld being formed, e.g., the
weld 54 shown in FIG. 3. The loops 159 can be positioned in a
variant of the channel 51 shown in FIG. 3 if the channel is a
through-hole positioned below a valley or lowest point of the
knurls 38 of the anvil head 36. Such a position can also help to
protect the loops 159 from damage during the vibration welding
process. However, in other embodiments channels (not shown) may be
formed in the knurl pattern at a depth which minimizes any
possibility of contact with the loops 159. Regardless of the
positioning or orientation of the loops 159 with respect to the
welding tool within which the loops are embedded, the loops should
be sufficiently insulated from each other.
[0034] Referring to FIG. 5, a method 100 is described with
reference to the structure shown in the various Figure. The method
100 can be used for heating a work piece and/or a welding
interface, e.g., the work piece 28 or welding interface 26 shown in
FIG. 1, during a vibration welding process using the welding system
10 shown in the same Figure. At step 102, a work piece 28 is
positioned between the sonotrode 24 and the anvil assembly 30, with
the work piece defining a welding interface 26. Step 102 may
include positioning the conductive tabs 42 of the battery 44 shown
in FIG. 1 and an interconnect member 46 of the same Figure adjacent
to each other and between the sonotrode 24 and the anvil assembly
30, with one of the welding interfaces being the innermost position
indicated in FIG. 1 by arrow 33.
[0035] Once positioned, at step 104 one or more induction heating
devices 40, 140 are energized to generate the eddy current (arrow
41) shown in FIGS. 1 and 3. The eddy current (arrow 41) heats the
welding tool, e.g., a portion of the anvil assembly 30, and/or the
work piece 28, to thereby increase the welding temperature at or
along a designated one of the welding interfaces 26 before
vibrations are transmitted by the sonotrode 24. The method 100 then
proceeds to step 106.
[0036] At step 106, a designated controller, e.g., the welding
controller 16 of FIG. 1 or the control module 50 of FIG. 2, uses a
closed loop feedback control approach to determine when welding
temperature at or along the designated welding interface 26 reaches
a calibrated temperature threshold, or falls within a calibrated
temperature range. For example, thermocouples may be used to
measure the temperature at the designated welding interface 26, or
in the vicinity of the welding interface, e.g., within the channel
51 of FIG. 3 or a variant thereof. The measured temperature can be
used by the designated controller in regulating a performance of
the induction heating device 40, 140 to maintain the temperature
within a calibrated range. The sonotrode 24 may be vibrating at
this point, with the friction heating from the knurls 27, 38 (see
FIG. 1) increasing the welding temperature in conjunction with heat
generated via the eddy currents (arrow 41) by the induction heating
device(s) 40, 140. Step 104 is repeated if the sensed temperature
is less than the calibrated temperature threshold, with method 100
otherwise proceeding to step 108.
[0037] At step 108, the weld is completed. The method 100 may then
repeat step 102 for a subsequent weld.
[0038] While the best modes for carrying out the invention have
been described in detail, those familiar with the art to which this
invention relates will recognize various alternative designs and
embodiments for practicing the invention within the scope of the
appended claims.
* * * * *